1. Field of the Invention
The subject invention relates to an apparatus and a method for testing oxidation resistant properties of lubricating oils for internal combustion engines and particularly turbocharged internal combustion engines. In a normal engine, the oil is exposed to relatively high temperatures and containments which can induce oxidation of the oil. A turbocharged engine, in addition, exposes the oil to the very high temperatures of the turbocharger shaft. When a hot engine is shut-off, the temperature of the turbocharger increases dramatically. Oil contacting very hot portions of the turbocharger can be rapidly oxidized and produce undesirable deposits on the internal metal surfaces. It can be understood that it is desirable to test oil under conditions simulating a hot engine.
The subject apparatus and method evaluates the oxidation resistent qualities of various oils under simulated engine and turbocharger conditions. The apparatus includes a reservoir holding a quantity of oil which is heated and exposed to contain such as moist air and nitrous oxide. These contaminants can cause formation of certain partially oxidized precursors which in turn can lead to deposit formation. The oil is pumped from the reservoir to a depositor apparatus which includes a heated rod over which the oil flows. Contact between the oil and the heated rod simulates the contact of hot oil with a turbocharger shaft of an engine. The temperature of the heated rod varies along its length due to the cooling effect of oil flowing along and over thereof. Deposits of oxidized products are formed on the surface of the rod and the quantity of the deposit can be determined by differential weight method. Also the appearance of the deposits can be studied to evaluate the oxidation resistance of lubricating oils.
2. Description of Related Art
There are several tests which are commonly conducted on lubricating oil to determine the oxidation effects of heating the oil. Equipment is available to perform infra-red spectra analysis on lubricating oils to detect various oxidation products. Other equipment is available to do a metals analysis or content on the oil. Neither of these tests very accurately reflects the environment of a hot engine and particularly a turbocharged engine.
It is known to test lubricating oil by passing lubricating oil over a heated rod. To a degree, this simulates an engine environment. However, it does not provide the two-stage thermal/oxidation effects of the subject apparatus and method. First, the subject apparatus and method uses an oil reservoir simulate to oil in an engine oil pan. The oil in the reservoir is heated and exposed to containments such as moist air and other oxidizing agents such as nitrous oxide. Secondly the contaminated oil is passed over a heated rod to stress the oil which tends to produce oxidation deposits on the rod. Applicant knows of no other test apparatus and method which provides such a two-stage thermal oxidation for lubricating oil as explained in more detail hereinafter.